1) Field of the Disclosure
The disclosure relates to optical fiber cables, and more particularly, to a self healing optical fiber cable assembly and method of making the same.
2) Description of Related Art
An optical fiber cable typically comprises a glass or plastic optical fiber that carries light along its length and various layers of protective and strengthening materials surrounding the optical fiber. Optical fiber cables are widely used in fiber optic communications which permit transmission over longer distances and at higher data rates than other forms of communications. Optical fiber cables may be used in space satellites and space environments, aircraft, sensors, light guides where bright light needs to be shone on a target without a clear line-of-sight path, imaging optics, and other suitable applications. An optical fiber is a cylindrical dielectric waveguide that transmits light along its axis by the process of total internal reflection. The fiber typically consists of a core, preferably a glass core, surrounded by a cladding layer. The cladding layer is typically used to reflect light back to the core because the cladding layer has a lower refractive index and to provide strength to the optical fiber. To confine the optical signal in the core, the refractive index of the core should preferably be greater than that of the cladding layer. With optical fiber cables, the cladding layer is typically coated with a tough resin buffer layer, which may be further surrounded by a jacket layer, usually a plastic material. These layers add strength to the fiber but do not contribute to its optical wave guide properties. Existing optical fiber cables may be assembled in a wide variety of sheathings. Optical fibers may be connected to each other by connectors or by splicing, that is, joining two optical fibers together to form a continuous optical waveguide.
Optical fiber cables can be very flexible but conventional fiber loss increases if the optical fiber cable is bent, such as the cable being bent around corners or wound around a spool. In addition, optical fiber reliability is dependant on the buffer layer and/or cladding layer damage, such as microcracks, that can grow with time when the optical fiber is exposed. Such microcracks can result in latent failures, failures in time, decreased robustness, decreased reliability, and shortened lifespan of the optical fiber and associated optical fiber cable and devices. Moreover, defects or damage to the buffer layer and/or cladding layer can occur as part of the manufacturing process, handling, and post-processing, and with time, can lead to cracks in the optical fibers. In addition, damage to the buffer layer and/or cladding layer can propagate into the optical fiber glass core. Buffer layer and/or cladding layer defects may be caused by fiber handling, mechanical motion, or rubbing, such as during the life of a space mission. Such defects may be difficult to screen out and may be a source for latent failures.
Known devices and methods exist for protecting and strengthening optical fiber cables and splices. For example, various cable protection materials may be applied around a portion of the optical fiber cables, and optical fiber splices may have protective layers or sleeves that can be heated/flowed around the splice for protection. However, such devices and methods can require additional thermal controls and/or controls on fiber routing which may result in increased complexity and costs and which may constrain the thermal environment for the optical fiber, thus resulting in decreased reliability. In addition, the cable protection materials often surround only the splice or a partial portion of the optical fiber cable and do not surround the entire length of the optical fiber cable, thus limiting the protection to the optical fiber cable. The life of an optical fiber cable is typically dependant on glass defect sizes which may be pre-screened with pull test breakage before the optical fiber cable is terminated and/or placed into an assembly/vehicle platform. Thereafter, the defects due to handling and/or mission environment may be difficult to remove or repair. Although damage or defects may be pre-screened to promote reliability, once a defect commences, time will result in failure of the optical fiber cable. Known optical fiber cables are not self healing to protect against such damage.
In addition, known optical fiber cables typically use thermal conditioning and/or mechanical and adhesive clamps or coupling devices to couple the fibers and cable components together, to achieve fiber alignment and controlled motion between the components, and to provide strain relief termination of the optical fiber cable. However, such known mechanical clamps or coupling devices may subject the optical fiber cable to excessive clamping or coupling pressure or damage, thus resulting in reduced light transmission. Moreover, insufficient thermal conditioning and/or clamping or coupling may permit undesirable movement of the optical fibers within the cable. Such movement may cause the optical fibers which are normally secured within the splice closure to “piston” in and out of the cable core. Pistoning expansion can create strain on the optical fibers and induce transmission losses. At the least, fiber bending around the splices may occur, and at the worst the optical fibers may be broken which results in devastation of the system. Such problems are particularly likely to occur in environments where significant temperature variations cause expansion and contraction, which result in clamping pressure variations.
In addition, optical fibers may also be susceptible to outgassing and decreased radiation resistance, such as may occur in aerospace applications. For example, optical fibers may be sealed and/or shielded with an adhesive or radiation resistant material, such as an epoxy/metal/ceramic material or epoxy filled with these materials, as part of an optical package. However, this can result in exposed adhesive within the intended package. Since many adhesives, such as epoxy, outgas or emit undesirable materials, such as water or solvents, this may result in contamination of the interior of the package with the resulting outgassed materials. Known methods and devices seek to avoid adhesives prone to outgassing entirely, attempt to reduce the outgassing, or remove the products of outgassing after sealing the hermetic package. However, such known methods and devices can be costly and can increase the size and weight of the optical fiber cable.
Accordingly, there is a need for a self healing optical fiber cable assembly and method of making the same that can provide advantages over known devices and methods.